Field of the Invention
The invention relates to a device for positioning an ink jet print head and a cleaning and sealing device, in particular in a postage meter and/or addressing machine.
In postage meters and/or addressing machines that have been on the market until now, printing is primarily carried out by ink rollers or thermal print heads.
Recently, efforts have been directed toward exploiting the advantages of ink jet printing in the field of applying postage and/or addressing mail by machine. The printing is carried out in a contactless manner through the use of ink jet print heads, as is seen in German Patent DE 44 24 771 C1 and German Utility Model DE 94 20 734 U1.
In that connection, a postage meter has been proposed in German Patent DE 196 05 014 C1, corresponding to U.S. Pat. application Ser. No. 08/791,630, filed Jan. 31, 1997, in which letters or envelopes are fed standing upright, tilting slightly to the rear, with the aid of a conveyor belt. The letters or envelopes rest there on a guide plate, in which a printing window is provided and in which the ink jet print head is fixedly installed. The letter or envelope is moved past the printing window or ink jet print head and during that time is imprinted on the side facing away from the observer.
However, the problem of ink jet print head cleaning and sealing is not addressed therein.
In conventional office printers with ink jet print heads, the recording medium and the ink jet print head are moved in alternation toward one another in orthogonal directions, with the spacing between the two being constant. The motion of the ink jet print head is effected as a rule in a forced guide crosswise to the ink ejection direction, or parallel to the plane of the recording medium.
That is also the case when the ink jet print head is cleaned and/or sealed off during certain intervals when no printing is being carried out.
To that end, the ink jet print head is moved, by the same drive mechanism as for printing, into a cleaning and sealing position laterally outside the printing position, and it remains in that position while a cleaning and sealing device is moved toward it and docked, as is seen in U.S. Pat. No. 4,533,927. The motion of the cleaning and sealing device is effected through the use of a lever system, without an additional drive mechanism, by utilizing the print head motion that extends parallel to the plane of the recording medium.
That principle cannot be adopted in the present structure, because of the different guidance of the print medium and because of the ink jet print head which is disposed stationarily for the printing process.
In another known configuration, for which reference is made to German Patent DE 36 08 912 C2, the ink jet print head on one hand is supported on guide rods so as to be translationally displaceable parallel to the plane of the recording media, which corresponds to its working position, and on the other hand is also supported rotatably and eccentrically in a drive housing. Through the use of the drive housing, the ink jet print head can be selectively rotated into a working position, a cleaning position, or a position of repose with sealing, and can be displaced in the ink ejection direction or contrary thereto.
In the cleaning position, priming can be carried out with manual tripping, and the nozzle surface of the ink jet print head can be wiped off through the use of a scraper.
In the position of repose, the nozzle surface of the print head is pressed against a diaphragm cap and sealed off in that way.
Aside from the fact that manual tripping is no longer conventional in modern machines, there is also the risk in the case of accelerated motion that ink will be unintentionally thrown off by centrifugal force, or that in the contrary direction of motion the ink jet print head will aspirate air, causing the ink meniscus to detach.
Finally, a device for cleaning an ink jet print head is also known from International Patent Application WO 96/15908 A1, in which the ink jet print head is secured so as to be pivotable out of a printing position into a cleaning position and/or sealing position and back again. A cleaning and sealing device is also disposed behind the guide plate but in such a way that it is linearly adjustable toward and away from the ink jet print head.
The cleaning and sealing device includes a sealing cap adapted to the ink jet print head, with suction slits for each row of nozzles, and it also includes a transversely adjustable wiper lip and a downstream suction pump. In the sealing cap, a vacuuming region is also provided on one end, with a central suction opening for the wiper lip. The wiper lip is adjusted through the use of a spindle drive.
The goal of the invention is to improve the print quality.